Work proposed here will investigate the specificity of odorant recognition in the malaria mosquito Anopheles gambiae and correlate specific odor stimuli with quantifiable physiological and behavioral responses. A multi-investigator effort will be undertaken that will integrate complementary expertise in various relevant fields toward the common goal of thoroughly understanding the chemosensory system and chemosensory-mediated behavior of Anopheles gambiae. Odor recognition specificity is very likely encoded in both odorant binding proteins (OBPs) and odorant receptors (ORs). We will carry out localization studies of OBPs and ORs by immunocytochemical and in situ hybridization assays on antennal sections to investigate the hypothesis that optimal tuning of odorant receptor neurons to a certain odor may be achieved by the co-expression of a matching combination of OBPs and ORs in defined olfactory sensilla. Because OBPs represent the first proteins of the olfactory system to encounter and bind odor molecules, in vitro expressed OBPs will be used in high-throughput screening assays to identify natural ligands and deduce binding capacities for known and newly identified ligands. Computer modeling studies combined with mutagenesis approaches will define the binding pocket and predict modified ligands with improved properties. In vivo validation of all in vitro studies will be obtained through electrophysiological and behavioral assays employing female mosquitoes that express a normal complement of OBPs or are deficient in specific OBP expression as a result of RNAi-mediated knockdown. Knowledge gained from this multi-disciplinary approach will lead to the identification of chemicals, which can interfere with host seeking behavior by female mosquitoes, thus reducing the incidence of contact between the human host and the parasite vector.